The present disclosure relates to a DC-DC converter, and more particularly, relates to bootstrapping of an on-drive voltage of a high-side switch in a DC-DC converter.
As DC power sources for various electronic equipments, switching-type DC-DC converters have been widely used. In general, in a DC-DC converter, switching control is performed to a high-side switch and a low-side switch which are connected in series between an input voltage and the ground, and electric energy stored in an inductor is smoothed by a smoothing capacitor, thus generating an output voltage.
There are cases where the high-side switch is comprised of an n-channel MOSFET for the purpose of reducing the size and improving the performance of the DC-DC converter. In such a case, a bootstrap circuit is provided, since an on-drive voltage of the high-side switch has to be equal to or higher than an input voltage. The bootstrap circuit includes a capacitor connected to a connection point of the high-side switch and the low-side switch, and the on-drive voltage of the high-side switch is pulled up by a charged voltage of the capacitor.
In general, a diode is provided between the capacitor and a power supply so that the charge of the capacitor does not flow in a reverse direction towards the power supply during bootstrapping of the on-drive voltage of the high-side switch. Configurations in which a switching transistor whose voltage drop is small is provided, instead of the diode, to prevent reduction in charging voltage of the capacitor have been known (see, e.g., Japanese Patent Publication No. 2007-195361).